Variable displacement hydraulic piston pumps and motors conventionally include a plurality of pistons slidable in a cylinder block coupled to a shaft that is rotatable within the machine housing. The pistons engage a yoke that is pivotally mounted to the housing by laterally spaced saddle bearings and engaged by a hydraulic piston or other suitable means for controlling displacement of the pistons within the cylinder block as the cylinder block rotates about the axis of the shaft. The cylinder block cavities in which the pistons are disposed are coupled by a valve plate or other suitable means to fluid inlet and outlet ports in the housing. The present invention deals with construction of the saddle bearings, which are lubricated by hydraulic fluid at case pressure within the machine housing.
The saddle bearings may be of non-rolling element construction as disclosed in U.S. Pat. No. 4,862,789, or of rolling element (roller or needle bearing) construction as in the present application. When a rolling element saddle bearing is employed, the roller retainer or cage is free during assembly to travel outside of the boundary of the inner and outer bearing races. It would be advantageous to provide facility to time the three arcuate bearing components (the cage and the inner and outer races) during assembly to prevent the cage from being positioned incorrectly. It is therefore a general object of the present invention to provide a rolling element saddle bearing of the described character having such facility for positioning and retaining the bearing elements with respect to each other during the assembly process.
A variable displacement hydraulic piston machine in accordance with the present invention includes a shaft mounted for rotation within a housing, a plurality of pistons in a cylinder block coupled to the shaft, a yoke engaged by the pistons for controlling displacement of the pistons in the cylinder block, and a saddle bearing pivotally mounting the yoke to a base within the housing. The saddle bearing includes arcuate inner and outer bearing races fixed to the yoke and the housing base respectively, a plurality of rolling elements captured by a cage or retainer between the races, and a timing lever positioning and retaining the races and the cage with respect to each other. The timing lever has a central portion pivotally mounted to the bearing between the bearing races, and opposed end portions pivotally received in the housing base and yoke. Thus, the lever automatically positions the bearing elements with respect to each other and with respect to the housing base and yoke, and limits movement of the various elements with respect to each other during the assembly process and operation. In the preferred embodiments of the invention, the opposed end portions of the timing lever have pan-spherical bearing heads that are slidably received in associated openings in the yoke and housing base. The central portion of the timing lever is pivotally mounted either to the cage or on one of the rolling elements themselves. The bearing races may have respective arcuate slots through which the opposed ends of the timing lever extend into associated openings in the yoke and housing base.
In accordance with another aspect of the present invention, there is therefore provided a saddle bearing suitable for use in mounting a yoke in a variable displacement hydraulic piston machine, as well as other similar applications. The bearing includes arcuate inner and outer bearing races, a plurality of rolling elements and a cage capturing the elements between the races for rolling engagement with the races. A timing lever has a central portion pivotally mounted between the bearing races, and opposed end portions extending from the central portion for receipt in structure between which the saddle bearing is to be mounted. In this way, the timing lever automatically positions and retains the races and cage with respect to such structure.